The degree of coherence of the supercontinuum(SC) directly determine the resolution and the precision in many optical apparatus, so how to achieve highly coherent SC is one of the focuses in nonlinear optics. It is shown that modulation instability (MI) is the key element that influences the coherence of SC. Therefore an effective way of achieving coherent SC is to avoid MI and to use other nonlinear effects such as self-phase modulation (SPM). We design a kind of photonic crystal fiber (PCF) which has an all-normal group velocity dispersion (GVD) profile. After numerical investigation on the generation of SC in the PCF we obtain the degrees of the SC in different lengths. Results indicate that for the generated SC by pumping 50 cm of this PCF with TFWHM=400 fs unchirped pulse Gaussian pulse can realize high coherence in the entire broadening area on condition that relative power is larger than -80 dB.